The invention relates to a steering rack housing for a power steering system which surrounds a steering rack in a tubular manner and comprises at least a hydraulic region and a mechanical region as well as an inner supporting bearing.
Rack-and-pinion steering systems are used in motor vehicles for converting the rotating steering movement applied through the steering wheel into a rectilinear movement for pivoting the vehicle wheels to be steered. In this case, a servo drive, which can be disposed at suitable locations within the steering power train, is used for steering power assistance.
In the case of a rack-and-pinion steering system, the end of the steering column is connected to a pinion engaging the steering rack and laterally displacing it when the steering system rotates. A track rod is respectively connected to both ends of the steering rack through a ball joint. The extremely low wear has ensured the widespread use of the rack-and-pinion steering system. Rack-and-pinion steering systems have a good feedback and a very good resilience.
Usually, steering rack housings consist of aluminum and are manufactured by die casting. Machining is required after casting, for example in order to be able to mount the pinion unit on the steering rack housing; contact surfaces are also milled in for the parts to be mounted. Blind bores and through bores for attachment purposes are also produced.
However, steering rack housings made from steel are also known. Compared to the usual aluminum steering-gear housings, full-steel housings have a number of advantages including a higher rigidity and toughness of the material. The perceived steering precision is noticeably enhanced by the more rigid steel housing. Another advantage is the compact and cost-effective routing of hydraulic lines of the steel housing, in which the screw interfaces can be omitted. The housing, which can be flexibly adapted to different types of vehicle, is produced as a welded structure from formed pre-configured precision steel tubes with strengths, depending on the degree of forming, of 450 to 650 N/mm2. A special galvanic coating ensures corrosion protection. The welded-on hydraulic supply lines enable an optimal adaptation to the construction space in the vehicle.
Steering rack housings comprise a mechanical region and a hydraulic region. The mechanical region is the region in which the region of the steering rack moves which is provided with teeth and which engages the pinion. The pinion engagement region is therefore located in the mechanical region of the steering rack housing. In contrast, the hydraulic region is the region into which the steering rack also extends but usually does not have any toothing. Within the hydraulic region, the steering rack is connected to a displaceably mounted piston member on each of whose end faces one cylinder chamber, respectively, is formed. When the steering wheel of the vehicle is turned, a control valve is actuated so that hydraulic oil flows into one of the cylinder chambers, respectively, whereby the piston and thus the steering rack are displaced in the cylinder. The displacement of the piston caused by the hydraulic oil serves as a force augmentation for the movement of the steering rack. To this end, the control valve and the steering rack housing are interconnected through hydraulic lines, so that, depending on the direction of rotation of the steering wheel, one or the other cylinder chamber can be filled with hydraulic oil or emptied.
A supporting ring or supporting bearing, which transmits the hydraulic internal forces into the steering rack housing and which generally also retains a sealing member, for example an O ring, is usually disposed between the mechanical region and the hydraulic region. In order to offer a point of force application to the supporting bearing, the steering rack housing has in this area a peripheral constricted portion which enables a positive fit with the supporting ring. The fabrication of the constricted portion entails relatively large efforts and correspondingly high costs.